Abstract Humans have greatly increased and unbalanced the concentration of ions in freshwater ecosystems (a phenomenon termed "freshwater salinization"). This was already reported as a major water quality problem in the 1930's, but it had been largely neglected by policy-makers, water managers and scientists until the 2000s. Traditionally, freshwater salinization was mainly associated with rising saline groundwaters and irrigation in arid lands, but during the last 15 years many other causes of salinization (e.g. road salt, resource extraction, industrial and urban wastewaters) have emerged all over the world. This has led to a proliferation of studies on the topic that have shown how freshwater salinization greatly reduces aquatic biodiversity, placing it among the top drivers of biological degradation. Here I will summarize what we know so far about the causes of freshwater salinization and its impacts on ecosystems and human welfare, and I will talk about pressing research needs. Some of the questions that need to be tackled and that I will discuss here are: What is the spatial extent of freshwater salinization? How do ions differ in their toxicity to aquatic biodiversity? How does salinization interact with other stressors occurring in freshwater ecosystems? What are the sub-letahl effects of freshwater salinization and what are the implications for trophic interactions? What is the impact of freshwater salinization on ecosystem functioning and services? Does freshwater salinization pose a risk to human health? Answering these questions is crucial to advance towards a proper management and regulation of this global environmental issue. Given future prediction of increased water demand and climate change (e.g. sea-level rise, drought intensification in some regions), actions to prevent, mitigate and remediate freshwater salinization should be implemented as soon as possible.

Advanced planning and management of urban lakes and ponds as a part of Integrated BGS (Blue Green Solution)

Abstract
Traditional approach in urban planning requires that we "protect the nature/environmeet" and this usually meant at high irrecoverable cost. According to the Blue Green Solutions (BGS), recently developed within the EU BGD (Blue Green Dream) project, the next generation planning methodology uses "inverse solutions". In this methodology, insetad of “protecting nature”, we bring nature (actually NBS - Nature Based Solutions) to urban enviroment to protect us, urban dwellers. In this way the nature ia also protected but in a more sustainable fashion. As opposed to conventional /opportunistic planning, application of our innovative planning and implementation tools such as GDPM (Goal Driven Planning Matrix) and evidence-based support is used for planning of urban amenities and infrastructure. This includes water, environment, energy, greenery, eco-systems and their services, reduction of natural disasters (flood, drought) and antrhopogenic causes of urban heat islands, water and air pollution by catering for sustainability and resilience to climate changes nad waether extremes.. These are based on engagement of planning and other professionals, all relevant stakeholders as well as local and central government bodies, supporting policy makers from the very early stage of pre-planning. This lecture presents the new planning methodology and the new role of urban water bodies such as lakes, ponds, urban streams, groundwater aquifers, coastal waters. Presented will also be quantified interactions of these asstes with other urban contents and integrated management of thier functions as well as environmental, financial and other benefits of this approach. Multifunctional beneficial applications will be illustrated by several examples: (i) urban park’s stream, used as multifunctional biotop, seasonal recretaional facility, interacting with groundwater aquifer for urban flood mitigation, (ii) program for cean-up of tens of thousands of urban lakes, (iii) innovative (urban metabolic hub) wastewater treatment technology supporting urban landscaping and streetscape, urban amenites and reducing negative impacts of climate changes, (iv) multifunctional urban stream clean-up and urban stream rehabilitation program, (v) real time urban pluvial flood forecast and management program in interactions with multifunctional elements of WSUD (Water Sensitive Urban Design), uprgarded to meet the BGS planning and management criteria.

Ecological stoichiometry in detritus-based headwater streams: current knowledge and perspectives

Abstract
Ecological stoichiometry (ES) is a unifying conceptual framework that focuses on how proportions of elements (in particular carbon, nitrogen, and phosphorus) affect organisms and ecosystems. A central tenet of ES is that elemental imbalances between resources and the requirements of organisms determine properties and drive ecological processes at all levels of biological organization, ranging from ecophysiology to population and community dynamics to ecosystem processes. To date, most ES studies have been directed towards the understanding of the herbivore-primary producer interactions. Yet, due to the generally low nutrient content of detritus, stoichiometric imbalances should be maximized at the detritus-decomposer interface. Forested headwater streams represent typical detritus-based ecosystems, where allochthonous detritus (leaf litter, woody debris, soil-derived dissolved organic matter) represent the main source of energy at the basis of food webs. During this presentation, I will propose a quick review of current knowledge on stoichiometric controls of headwater stream functioning. First, despite the large availability of data on detritus elemental compositions and their consequences for detritus decomposition, only a few studies investigated the elemental composition of microbial decomposers (bacteria and aquatic fungi). Due to their elemental plasticity, these decomposers are able to largely and quickly modify leaf litter elemental quality. Second, a growing number of studies investigated the relationships between detritus elemental composition and detritivores life-history traits, showing that elemental imbalances might represent a major determinant of secondary production in these ecosystems. The use of nutrient immobilization capabilities of microbial decomposers might represent an important step towards the proper experimental quantification of the roles of stoichiometry in detritus-based ecosystems, avoiding most biases generally arising in such studies. Finally, I will present the current gaps and some perspectives for understanding all the consequences of stoichiometry for detritus-based headwater streams functioning. In particular, upscaling results from studies carried out at the organism scale to population dynamics and community structures certainly represent a crucial step, requiring specific investigations.

AbstractAndean-Patagonian transparent ultraoligotrophic lakes have a particular microbial food web, with the presence of large mixotrophic ciliates. These organisms exhibit different features that allow them to colonize either the epilimnion (Stentor araucanus) or the metalimnion (Ophrydium naumanni). S. araucanus, a dark pigmented (stentorin) species resistant to ultraviolet radiation, is always present in the upper layers of the epilimnion. This species needs high light supply to maintain endosymbiotic algal photosynthesis and was favored during years of shallower thermocline and high epilimnetic mean irradiance. In contrast, O. naumanni prefer the metalimnetic layers and was more abundant in years with deeper thermoclines, being photosynthetically efficient at low light intensities but susceptible to photoinhibition at epilimnetic light irradiances. This species dominates the phothosynthetic biomass in the deep chlorophyll maxima of these lakes. Analysis of food vacuoles revealed a weak niche overlap, thus light climate, created by temporal or spatial variations in thermocline depth, is a key factor modulating relative success these mixotrophic ciliate species. Overall these species are stoichiometrically, carbon to nutrients, more balanced than the bulk seston, but the mechanisms by which each species regulates the elemental balance differ. S. araucanus regulates the light inside the organism, thus regulating the carbon fixation, while O naumanni increases bacterivory with light, thus increasing phosphorus uptake. The low Carbon:nutrient ratio of these organisms would represent a very good food source for predators. The link between mixotrophic ciliates and zooplankton revealed that they are eaten by the cyclopoid copepod Mesocyclops araucanus. However, the stentorin pigment of S. araucanus increases oxidative stress in the predator. Combining field and laboratory analysis we showed that the wide amplitude of the diel vertical migration protects the copepods from stentorin-induced oxidative stress during daytime. Thus, a compound of a mixotrophic ciliate prey item can influence the vertical behavior of predators in order to minimize the negative effect.

Restoration, watershed context, and biogeochemical processes: from streams to wetlands

AbstractDespite the essential role that water plays in life, humans have degraded ecosystems to such an extent that the quantity or quality of water in streams, rivers and wetlands is at risk worldwide. In response, efforts to restore degraded aquatic systems have grown dramatically. While many restoration projects have focused primarily on ecological structure, restoration in practice has its scientific roots firmly in ecology and related fields that emphasize the role of ecological processes and landscape context in determining the self-sustainability of ecosystems. Without recovery of basic ecosystem processes including interactions at watershed scales, restoration is unlikely to lead to self-sustainability. I will provide a brief overview of restoration approaches and outcomes in the context of hydrologic and biogeochemical processes followed by several case studies as examples. The talk will end with a brief discussion of research needs to advance restoration of aquatic ecosystems. The first case focuses on streams that have been degraded by high population densities and associated impervious cover. While the primary approach to restore urban streams has been to manage the riparian zone or reconfigure channel form, more recent efforts have involved a combination of watershed, channel, and riparian practices that come closer to restoring processes. I will describe research to measure hydrologic, nutrient, and sediment retention processes before and after such projects and the insights we have gained from such research. The second case focuses on upland wetlands that vary in their hydrologic connectivity to perennial stream networks. Many of these wetlands have been altered by human modification including ditching. In some regions, efforts have been undertaken to hydrologically restore wetlands by plugging ditches so that wetlands do not drain quickly but hold surface water a larger fraction of the year. A focus on hydrologic connectivity is important because fluxes of materials from wetlands to downstream perennial waters may be significant. I will describe research to quantify temporal hydrologic connectivity of wetlands and intermittent channels to perennial stream networks and how this influences the concentration and composition of dissolved organic matter to downstream waters. The goal is to understand if hydrologic connectivity influences other processes such as microbial production.

AbstractHydrologic connections in the landscape determine ecological patterns and rates of ecosystem processes at local to global scales. Management and policy decisions, on issues ranging from hydropower development to nutrient loading, are often made in the absence of information on how these hydrologic connections structure the landscape. We are further challenged to develop a predictive understanding of how climate-mediated changes in hydrologic connectivity affect the environment. We use the term hydrologic connectivity here to refer to water-mediated transport of matter, energy and/or organisms within or between elements of the hydrologic cycle. Two examples from the wet Neotropics illustrate the importance of long-term research on this issue. The first case study highlights lowland streams draining Costa Rica’s Caribbean slope, some of which receive interbasin flows of regional subsurface groundwater. Regional groundwater is rich in phosphate and bicarbonate, which stimulate algal and insect growth rates. and buffer receiving streams against pH declines, respectively. Lowland streams, that do not receive regional groundwater, experience pH declines (as low as 4 for several months) as a result of the influx of local CO2-rich groundwater following dry periods often associated with ENSO events. This is of concern given that climate models predict declining rainfall in the dry season and an increase in the frequency of ENSO events. The second case study focuses on Puerto Rico, where large dams block the access of native migratory fishes and shrimps to headwater streams that drain 23% of the islands mountainous interior. Extirpation of native biota above dams results in decreased leaf decomposition rates and increased algal biomass at a landscape scale. While streams draining El Yunque National Forest in northeastern Puerto Rico are relatively free-flowing and provide habitat for native biota, they are increasingly tapped for municipal water supplies. This results in reduced stream flow and severe reductions in hydrologic connectivity between the mountains and the sea during droughts. Predicted increases in the incidence of droughts and hurricanes underline the vulnerability of native fish and shrimp in the last relatively free flowing rivers on the island. In summary, the complexity of climate-driven changes in hydrologic connectivity creates interacting layers of emergent ecological effects that become apparent through long-term studies on decadal time-frames.

Fish as local stressors of Pyrenean high mountain lakes: arrival process and impact on amphibians and other organisms

Pyrenean high mountain lakes are naturally fishless due to hydrographic barriers that have prevented the natural colonisation of fish species from lower streams. However, there have been numerous introductions of trout to such ecosystems, both in historical and recent periods. Minnows have also been introduced recently as a result of recreational fishing with live-bait. Trout and minnow introductions can cause large ecological problems and ecosystem change in high mountain lakes, since both fish occupy the top of a lake’s food chain. The study had two objectives. First, we wanted to investigate which particular anthropogenic and environmental factors best explained fish presence in the Pyrenean lakes. For that purpose we collected data on trout and minnow occurrence from 520 high mountain lakes >0.5 ha in the southern Pyrenees. The second objective was to investigate the effect of introduced fish on faunal groups such as amphibians, conspicuous macroinvertebrates and planktonic crustaceans. We also considered whether there was a trophic cascade from fish to the littoral epilithic community of these ecosystems. For that purpose we sampled 1736 Pyrenean high mountain lakes and ponds at different levels of intensity. The distribution of Salmo trutta in the lakes of the southern slopes of the Pyrenees was best explained by both anthropogenic factors and lake characteristics, while only anthropogenic factors linked to recreational fishing were associated with the distribution of the exotic trout Salvelinus fontinalis and Oncorhynchus mykiss. In the case of minnow occurrence, previous presence of trout in the lake was the most explanative variable, confirming its association with recreational fishing using it as live-bait. Fish presence was linked with the disappearance of most amphibian species. Minnows also showed a sizeable impact on the pelagic habitat, reducing the abundance of some herbivorous species of zooplankton that appeared to be unaffected by trout. In the case of amphibian species, we found that, although introduced fish had a high local impact, western-eastern patterns of some environmental variables are the main drivers of amphibian species distribution at Pyrenean range scale. In addition, we confirmed the presence of a littoral trophic cascade that defines most of the characteristics of the littoral epilithon of Pyrenean high mountain lakes and ponds through fish predation of tadpoles and hence, by a drastic reduction of grazing activity.